MWJL 5.2

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Igneous Rocks

Vocabulary


Extrusive Rock: Igneous rock that forms from lava that is on the surface of the earth.
Intrusive Rock: Igneous rock that forms from magma that is hardened beneath the surface of the earth.
Porphyritic texture: A kind of texture when giant crystals are scattered right in a background of smaller crystals.

Outline


Characteristics of Igneous Rock

  • Origin
    • Extrusive Rock
      • It is igneous rock formed above the earth's surface.
    • Intrusive Rock
      • It is igneous rock formed beneath the earth's surface.
  • Texture
    • The texture of an igneous rock depends on the size and shape of its mineral crystals.
      • Extrusive and Intrusive rocks usually have different textures.
        • Intrusive rocks have larger crystals than extrusive rocks.
        • Some rocks can have two textures.
          • Rocks can have two textures because it cools in two stages.
  • Mineral Composition
    • Magma that is high in silica usually forms rocks that are light colored.
    • Magma that is low in silica usually forms rocks that are dark colored.

Uses of Igneous Rocks

  • Lots of igneous rocks are hard and durable
    • They have used this type of rock for building materials.
      • Ancient Egyptians used granite for statues.
    • Igneous rock such as basalt, pumice, and obsidian also have important uses.
      • Basalt is crushed to make gravel that is used in construction.
      • pumice is a good abrasive for cleaning and polishing.
      • Perlite is often mixed with soil for starting vegetable seeds.

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